The present invention is related to the field of bath systems for processing semiconductor wafers and, more particularly, bath systems using sonic energy for processing such wafers.
In the present bath systems, a container is loaded with a cassette of semiconductor wafers and a processing liquid is pumped and filtered for recirculation through the container. Typically in a semiconductor fabrication area, there are several bath systems, each of which contains different liquids for processing the semiconductor wafers. The different liquids may include water with varying degrees of chemical contamination for sequentially rinsing the wafers after a processing step. One such bath system, for example, is disclosed in U.S. Pat. No. 4,955,402, which issued on Sep. 11, 1990 to the present inventor.
Associated with these bath systems are the costs for purchasing several systems for each fabrication area, and the costs of the processing liquids for the bath systems. There are also the cost associated with the handling of the wafers as they are moved from one bath to another, i.e., the time consumed in moving the wafers and the losses which inevitably occur in handling the wafers.
One proposal to overcome these deficiencies has been a multiple processing bath system. In such systems, the wafers are left in the bath container as the chemistry of the liquid is changed. Gas is bubbled through the liquid in the container to change the chemistry of the liquid.
Another recent development in semiconductor bath systems is the use of sonic energy which is directed against the wafers in the processing liquid. The sonic energy has been found to not only deliver kinetic energy for mechanically "scrubbing" the surfaces of the wafers, but also helps with the desired chemical reaction at the wafer surface/processing liquid interface.
However, bath systems using such sonic energy have not had optimal performance. In some systems, the sonic transducers have been mounted on the outside of the processing container with inefficient and uneven delivery of sonic energy to the wafers. To counter this problem, other systems have placed the sonic transducers on the inside of the processing container thereby exposing the transducers and their electrical connections to the sometimes corrosive properties of the processing liquid. This has sometimes lead to the contamination of the wafers. Furthermore, such systems have not been able to operate at higher temperatures from the failure of the bonding used to mount the transducers at those temperatures.
To overcome these problems, the present invention provides a unique system capable of multiple processing of semiconductor wafers with sonic energy which is delivered in an efficient and non-contaminating manner. Wafer handling is substantially reduced with the attendant savings of a single bath system.